Solar Plane Passes 24-hour Endurance Test

Stores enough sunlight to stay aloft overnight

This sleek aircraft, the Solar Impulse HB-SIA, remained aloft for an entire day in July, completing the first-ever night flight for a solar plane. During the day, the 11 628 monocrystalline silicon solar panels blanketing its wings—63 meters from tip to tip—generated enough electricity to power its four 7.46-kilowatt motors and top up its 70 polymer lithium batteries. The batteries' 96-kilowatt-hour total capacity was enough to keep the plane cruising along at an average of 70 kilometers per hour between dusk and dawn. Designers are working on a version with lighter batteries that will circle the globe without touching down.